Understanding the size and shape of colloidal particles is essential for B.Pharm students studying drug delivery, formulation, and stability. Particle size (nanometers to micrometers) and morphology (spheres, rods, plates, ellipsoids, aggregates) directly influence diffusion, sedimentation, optical scattering, surface area, and biological interactions. Key concepts include hydrodynamic radius, polydispersity, Rayleigh and Mie scattering, zeta potential, DLVO theory, and techniques like DLS, TEM, SEM, SAXS and ultracentrifugation. Mastery of how size and shape affect colloid stability, drug release, cellular uptake, and rheology will improve formulation design and quality control. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which size range typically defines colloidal particles?
- 0.1 nm to 1 nm
- 1 nm to 1 µm
- 1 µm to 1 mm
- 1 mm to 1 cm
Correct Answer: 1 nm to 1 µm
Q2. What is the hydrodynamic radius measured by dynamic light scattering (DLS)?
- Actual geometric radius observed in TEM
- Radius derived from diffusion behavior in solution
- Radius calculated from molecular weight only
- Radius determined by sedimentation rate in ultracentrifuge
Correct Answer: Radius derived from diffusion behavior in solution
Q3. Which scattering regime applies when particle diameter is much smaller than the wavelength of light?
- Mie scattering
- Rayleigh scattering
- Geometric optics scattering
- Raman scattering
Correct Answer: Rayleigh scattering
Q4. How does light scattering intensity scale with particle diameter in the Rayleigh regime?
- Proportional to diameter
- Proportional to diameter squared
- Proportional to diameter cubed
- Proportional to diameter to the sixth power
Correct Answer: Proportional to diameter to the sixth power
Q5. Which instrument provides direct images of particle shape and internal structure at nanometer resolution?
- Dynamic light scattering (DLS)
- UV-Vis spectrophotometer
- Transmission electron microscopy (TEM)
- Zeta potential analyzer
Correct Answer: Transmission electron microscopy (TEM)
Q6. Polydispersity index (PDI) from DLS indicates:
- Chemical composition of particles
- Degree of particle size distribution heterogeneity
- Particle density value
- Surface charge magnitude
Correct Answer: Degree of particle size distribution heterogeneity
Q7. Aspect ratio of a colloidal particle describes:
- Ratio of surface charge to mass
- Ratio of longest to shortest particle dimension
- Proportion of crystalline to amorphous regions
- Ratio of hydrodynamic to geometric radius
Correct Answer: Ratio of longest to shortest particle dimension
Q8. Which effect increases with decreasing particle size for a fixed mass of colloid?
- Settling velocity
- Surface area to volume ratio
- Gravitational force per particle
- Bulk density
Correct Answer: Surface area to volume ratio
Q9. In Stokes’ law for sedimentation, which property is NOT directly involved?
- Fluid viscosity
- Particle radius
- Particle density
- Particle zeta potential
Correct Answer: Particle zeta potential
Q10. Which shape would typically show the slowest sedimentation rate assuming equal volume: sphere, rod, disk, or compact aggregate?
- Sphere
- Rod
- Disk (platelet)
- Compact aggregate
Correct Answer: Disk (platelet)
Q11. Which technique measures zeta potential related to surface charge and electrophoretic mobility?
- Atomic force microscopy (AFM)
- Electrophoretic light scattering
- Scanning electron microscopy (SEM)
- Small-angle X-ray scattering (SAXS)
Correct Answer: Electrophoretic light scattering
Q12. Which phenomenon describes random motion of colloidal particles due to thermal energy?
- Brownian motion
- Diffraction
- Coagulation
- Electrophoresis
Correct Answer: Brownian motion
Q13. The Einstein relation links diffusion coefficient (D) to which parameters?
- Particle charge and ionic strength
- Temperature and friction coefficient
- Viscosity and centrifugal force
- Surface tension and contact angle
Correct Answer: Temperature and friction coefficient
Q14. Hydrodynamic diameter differs from geometric diameter because it includes:
- Only the particle core size
- Solvation layer and bound solvent molecules
- The dry powder porosity
- Optical refractive index only
Correct Answer: Solvation layer and bound solvent molecules
Q15. Which shape of nanoparticle generally has higher cellular uptake in many cell types?
- Spherical particles
- Large plates
- Long rigid rods
- Huge aggregates
Correct Answer: Spherical particles
Q16. DLVO theory combines which two interactions to predict colloid stability?
- Hydrophobic and covalent bonding
- Electrostatic repulsion and van der Waals attraction
- Magnetic attraction and steric hindrance
- Gravitational and osmotic pressure
Correct Answer: Electrostatic repulsion and van der Waals attraction
Q17. Steric stabilization of colloids is achieved by:
- High ionic strength to screen charges
- Adsorbing polymer or surfactant layers to prevent close approach
- Heating to induce Brownian motion
- Applying a magnetic field
Correct Answer: Adsorbing polymer or surfactant layers to prevent close approach
Q18. Which structural descriptor quantifies branching density in aggregates and influences rheology?
- Aspect ratio
- Fractal dimension
- Polydispersity index
- Hydrodynamic radius
Correct Answer: Fractal dimension
Q19. Mie scattering is most relevant when particle size is:
- Much smaller than light wavelength
- Comparable to or larger than light wavelength
- Only in the ultraviolet region
- Negligible for metallic particles
Correct Answer: Comparable to or larger than light wavelength
Q20. Which method separates particles by sedimentation coefficient and can give size distribution?
- Size-exclusion chromatography
- Analytical ultracentrifugation
- Fourier-transform infrared spectroscopy
- Zeta potential measurement
Correct Answer: Analytical ultracentrifugation
Q21. Anisotropic colloidal particles differ from isotropic ones mainly in:
- Chemical composition only
- Directional shape-dependent properties
- Electrical neutrality
- Being larger than 1 mm
Correct Answer: Directional shape-dependent properties
Q22. Which parameter increases the diffusion coefficient of a particle in solution?
- Increasing particle radius
- Increasing medium viscosity
- Increasing temperature
- Increasing particle density
Correct Answer: Increasing temperature
Q23. What does a high polydispersity index (PDI > 0.7) from DLS indicate?
- Uniform particle size
- Multiple size populations or broad distribution
- High crystallinity
- Strong electrostatic stabilization
Correct Answer: Multiple size populations or broad distribution
Q24. Which colloid shape tends to have the highest surface area per unit mass?
- Large smooth spheres
- Thin platelets or flakes
- Compact dense aggregates
- Solid cubes
Correct Answer: Thin platelets or flakes
Q25. Zeta potential magnitude typically indicates:
- Particle color
- Electrostatic stability against aggregation
- Exact particle size
- Viscosity of dispersion medium
Correct Answer: Electrostatic stability against aggregation
Q26. Which experimental technique yields topographical (3D) surface maps of single particles?
- Transmission electron microscopy (TEM)
- Atomic force microscopy (AFM)
- Dynamic light scattering (DLS)
- Nuclear magnetic resonance (NMR)
Correct Answer: Atomic force microscopy (AFM)
Q27. In formulations, reducing particle size generally leads to:
- Decreased dissolution rate
- Increased sedimentation rate
- Increased surface area and faster dissolution
- Complete elimination of aggregation
Correct Answer: Increased surface area and faster dissolution
Q28. Which factor does NOT strongly influence colloidal aggregation kinetics?
- Ionic strength of medium
- Particle concentration
- Particle shape
- Color of the particles
Correct Answer: Color of the particles
Q29. Hydrodynamic interactions and rotational diffusion become most important for which particle type?
- Perfectly spherical particles only
- Anisotropic (rod-like or plate-like) particles
- Single atoms in gas phase
- Bulk crystals
Correct Answer: Anisotropic (rod-like or plate-like) particles
Q30. Which measurement gives information about internal structure and electron density contrast of colloids?
- Small-angle X-ray scattering (SAXS)
- Ultraviolet absorbance only
- Electrophoretic mobility
- Refractive index increment
Correct Answer: Small-angle X-ray scattering (SAXS)
Q31. What happens to viscosity of a colloidal dispersion as particle concentration increases for non-interacting spheres?
- Viscosity decreases
- Viscosity remains constant
- Viscosity increases
- Viscosity becomes negative
Correct Answer: Viscosity increases
Q32. Which statement about hydrodynamic radius (Rh) vs actual radius is correct for non-spherical particles?
- Rh always equals the longest geometric dimension
- Rh represents an effective sphere radius that reproduces hydrodynamic behavior
- Rh is irrelevant for non-spherical particles
- Rh is identical to diameter measured by TEM
Correct Answer: Rh represents an effective sphere radius that reproduces hydrodynamic behavior
Q33. Which type of colloidal particle is most likely to demonstrate anisotropic optical properties?
- Perfectly spherical polymer beads
- Gold nanorods
- Homogeneous microcrystals
- Symmetric micelles
Correct Answer: Gold nanorods
Q34. Which property is critical when designing nanoparticle carriers for enhanced permeation across biological barriers?
- Particle color
- Size and shape to influence cellular uptake and permeability
- Electric power source
- Melting point of the drug
Correct Answer: Size and shape to influence cellular uptake and permeability
Q35. Which phenomenon leads to increased turbidity in a colloidal suspension?
- Decreased particle concentration
- Increased particle aggregation or larger particles
- Reduction in refractive index contrast
- Complete dissolution of particles
Correct Answer: Increased particle aggregation or larger particles
Q36. Which descriptor best characterizes plate-like colloids?
- High aspect ratio with one dimension much smaller than others
- Perfect symmetry in all three dimensions
- Low surface area per unit mass
- Always spherical
Correct Answer: High aspect ratio with one dimension much smaller than others
Q37. What is the primary reason small colloidal particles remain suspended rather than settling quickly?
- Strong magnetic forces
- High Brownian motion relative to gravitational forces
- Chemical reactions with solvent
- They are heavier than the medium
Correct Answer: High Brownian motion relative to gravitational forces
Q38. Differential centrifugal sedimentation separates particles mainly by:
- Surface charge
- Hydrodynamic diameter and density
- Optical absorption only
- Magnetic susceptibility
Correct Answer: Hydrodynamic diameter and density
Q39. Which change typically reduces electrostatic repulsion between charged colloidal particles?
- Decreasing ionic strength
- Increasing ionic strength
- Adding steric stabilizers
- Lowering particle density
Correct Answer: Increasing ionic strength
Q40. Which shape is most likely to pack densely and reduce free volume in a suspension?
- Irregular fluffy aggregates
- Close-packed spheres or ordered arrays
- Highly elongated flexible chains
- Thin dispersed platelets aligned randomly
Correct Answer: Close-packed spheres or ordered arrays
Q41. Which analytical method provides average radius of gyration (Rg) sensitive to overall particle mass distribution?
- Size-exclusion chromatography
- Static light scattering (SLS) or SAXS
- Zeta potential analysis
- Thermogravimetric analysis
Correct Answer: Static light scattering (SLS) or SAXS
Q42. How does particle shape influence drug release from particulate carriers?
- Shape has no influence on release kinetics
- Spherical shapes always release slower than rods
- Surface area, diffusion paths and orientation affect release rates
- Only chemical composition controls release
Correct Answer: Surface area, diffusion paths and orientation affect release rates
Q43. Which colloidal form typically shows shear-thinning behavior influenced by particle shape and interactions?
- Dilute ideal gas
- Concentrated suspensions of anisotropic particles
- Pure water
- Non-interacting low concentration spheres
Correct Answer: Concentrated suspensions of anisotropic particles
Q44. What is the effect of increasing the ionic strength on the electrical double layer thickness around a particle?
- Double layer thickness increases
- Double layer thickness decreases
- Double layer becomes positively charged only
- No effect on double layer thickness
Correct Answer: Double layer thickness decreases
Q45. Which particle attribute most directly affects the magnitude of van der Waals attraction between particles?
- Color of the particle
- Particle size and separation distance
- Ambient light intensity
- Smell of the dispersion
Correct Answer: Particle size and separation distance
Q46. For drug-loaded liposomes, which size range is often preferred to avoid rapid clearance by the reticuloendothelial system?
- Greater than 5 µm
- Approximately 100–200 nm
- Smaller than 1 nm
- Exactly 10 mm
Correct Answer: Approximately 100–200 nm
Q47. Which property best explains why rod-shaped bacteria and particles align in flow fields?
- Uniform spherical symmetry
- Anisotropic hydrodynamic drag and torque
- High zeta potential
- Color contrast with medium
Correct Answer: Anisotropic hydrodynamic drag and torque
Q48. Which technique is most suitable to determine particle shape population in a dry powder sample?
- Dynamic light scattering (DLS)
- Scanning electron microscopy (SEM)
- UV-Vis spectroscopy
- Electrophoretic mobility
Correct Answer: Scanning electron microscopy (SEM)
Q49. Which of the following increases the stability of colloidal suspensions against van der Waals attraction?
- Reducing surface charge
- Adding non-adsorbing salt
- Adsorbing bulky polymers for steric repulsion
- Heating to evaporate solvent
Correct Answer: Adsorbing bulky polymers for steric repulsion
Q50. Which factor would you adjust to shift scattering from Rayleigh to Mie regime for characterization?
- Use much shorter wavelength light or select larger particles
- Decrease ionic strength only
- Make particles more electrically charged
- Reduce temperature below freezing
Correct Answer: Use much shorter wavelength light or select larger particles
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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